1. Field of the Invention
Aspects of the present invention relate to color reproduction. More particularly, the present invention relates to a color-reproduction system and method that reproduces an image by changing various color attributes between display screens of different sizes.
2. Description of the Related Art
A wide variety display devices are being used in many aspects of our daily life. Recently, in addition to traditional CRT displays, mobile displays such as OLED and LCD mobile display devices are commonly used.
Especially, the mobile displays have developed dramatically and been widely applied in the mobile TV, mobile phone, PDAs, portable media players (PMPs) and others. The display industry has put many efforts to develop high quality displays having large color gamuts.
However, even if displays have a large color gamut, it's still not possible to faithfully reproduce color images due to device characteristics, viewing conditions and color shift in human perception.
Generally, the color generation for displays is different among different manufactures and even different models. The RGB color space generally employed for all displays does not take the color changes across different devices into account. In addition, the RGB color space does not take into account viewing conditions.
Consequently, the same image could appear significantly different on another display if employing gamut mapping in the RGB color space regardless of different device characteristics and different viewing conditions.
Therefore, in the conventional color reproduction method, color space conversion models have been employed to reproduce color imaging across different displays and viewing conditions.
For example, the GOG model and the PLCC model can be used to convert the image from device dependent RGB color values to device independent CIE (Commission Internationale de 1'Eclairage) tristimulus values XYZ. According to CIE color appearance models, XYZ values can further be converted to three color appearance attributes, luminance, chroma and hue composition, which are independent of complicated viewing conditions.
However, although the device characteristics and viewing conditions issue can be resolved through the above color space conversion models, the color shift in human perception has not been considered in the above traditional color reproduction method.
Scientific instruments will record the true color of an image irrespective of whether the display panel extends over a small area or a large area, but the humans will perceive its colors as being different if the display size is altered.
Further, the color shifting for an image also depends on the image content. For example, the shifting effect would be significant for the images having a large area of uniform color, and would be slight for the images having a small area of uniform color.
Consequently, human perception of the image will change correspondingly when the image size is altered, which is called “image size effect on color shift in human perception” or “image size effect” for short. Hence, there is a need for a new accurate color reproduction method for compensating for the image-size effect.
International Unexamined Patent WO2004/097353A1 discloses a method for compensating for the shift in the human perception of color which occurs when the color is seen on a small surface area (e.g., those found in paint sales brochures or drapery catalogues) as compared with when it is seen extending over a large surface area (e.g., walls, ceilings or curtains). The above patent provides a method of calculating the shifts of the luminance and chroma values generated by color size effect in human perception. However, it cannot be applied to color reproduction between displays due to the following.
First, the prior patent is employed in the physical color rather than self-luminous color displays. It was found that chroma shift does not depend on hue for physical colors while it is different in the self-luminous color system.
Second, the size ratio was fixed in the prior patent, wherein the color reproduction is implemented from a subtending view angle in the range of 2-50°. While, the displays have a wide variety of size, for example, the subtending view angle can be 100, 150, 400, 900, 1000, and others. However, since the prior patent has not been designed for the uniform color patch, it does not take the image content into account. However, since the color images shown in the displays are not uniform in color, the image content needs to be considered.